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feat: Add support for AES-GCM family #67

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Mar 24, 2020
Merged

feat: Add support for AES-GCM family #67

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2 changes: 2 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,8 @@ Currently the library supports:
* EncryptedData using:
* http://www.w3.org/2001/04/xmlenc#aes128-cbc
* http://www.w3.org/2001/04/xmlenc#aes256-cbc
* http://www.w3.org/2009/xmlenc11#aes128-gcm
* http://www.w3.org/2009/xmlenc11#aes256-gcm
* http://www.w3.org/2001/04/xmlenc#tripledes-cbc (Insecure Algorithm)

Insecure Algorithms can be disabled via disallowEncryptionWithInsecureAlgorithm/disallowDecryptionWithInsecureAlgorithm flags when encrypting/decrypting. This flag is off by default in 0.x versions.
Expand Down
36 changes: 33 additions & 3 deletions lib/xmlenc.js
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Expand Up @@ -78,6 +78,12 @@ function encrypt(content, options, callback) {
case 'http://www.w3.org/2001/04/xmlenc#aes256-cbc':
crypto.randomBytes(32, cb); // generate a symmetric random key 32 bytes length
break;
case 'http://www.w3.org/2009/xmlenc11#aes128-gcm':
crypto.randomBytes(16, cb); // generate a symmetric random key 16 bytes length
break;
case 'http://www.w3.org/2009/xmlenc11#aes256-gcm':
crypto.randomBytes(32, cb); // generate a symmetric random key 32 bytes length
break;
case 'http://www.w3.org/2001/04/xmlenc#tripledes-cbc':
crypto.randomBytes(24, cb); // generate a symmetric random key 24 bytes (192 bits) length
break;
Expand All @@ -100,6 +106,18 @@ function encrypt(content, options, callback) {
cb(null, encryptedContent);
});
break;
case 'http://www.w3.org/2009/xmlenc11#aes128-gcm':
encryptWithAlgorithm('aes-128-gcm', symmetricKey, 12, content, options.input_encoding, function (err, encryptedContent) {
if (err) return cb(err);
cb(null, encryptedContent);
});
break;
case 'http://www.w3.org/2009/xmlenc11#aes256-gcm':
encryptWithAlgorithm('aes-256-gcm', symmetricKey, 12, content, options.input_encoding, function (err, encryptedContent) {
if (err) return cb(err);
cb(null, encryptedContent);
});
break;
case 'http://www.w3.org/2001/04/xmlenc#tripledes-cbc':
encryptWithAlgorithm('des-ede3-cbc', symmetricKey, 8, content, options.input_encoding, function (err, encryptedContent) {
if (err) return cb(err);
Expand All @@ -114,7 +132,6 @@ function encrypt(content, options, callback) {
function encrypt_key(symmetricKey, encryptedContent, cb) {
encryptKeyInfo(symmetricKey, options, function(err, keyInfo) {
if (err) return cb(err);

var result = utils.renderTemplate('encrypted-key', {
encryptedContent: encryptedContent.toString('base64'),
keyInfo: keyInfo,
Expand Down Expand Up @@ -170,14 +187,17 @@ function decrypt(xml, options, callback) {
var encryptedContent = xpath.select("//*[local-name(.)='EncryptedData']/*[local-name(.)='CipherData']/*[local-name(.)='CipherValue']", doc)[0];

var encrypted = Buffer.from(encryptedContent.textContent, 'base64');

switch (encryptionAlgorithm) {
case 'http://www.w3.org/2001/04/xmlenc#aes128-cbc':
return callback(null, decryptWithAlgorithm('aes-128-cbc', symmetricKey, 16, encrypted));
case 'http://www.w3.org/2001/04/xmlenc#aes256-cbc':
return callback(null, decryptWithAlgorithm('aes-256-cbc', symmetricKey, 16, encrypted));
case 'http://www.w3.org/2001/04/xmlenc#tripledes-cbc':
return callback(null, decryptWithAlgorithm('des-ede3-cbc', symmetricKey, 8, encrypted));
case 'http://www.w3.org/2009/xmlenc11#aes128-gcm':
return callback(null, decryptWithAlgorithm('aes-128-gcm', symmetricKey, 12, encrypted));
case 'http://www.w3.org/2009/xmlenc11#aes256-gcm':
return callback(null, decryptWithAlgorithm('aes-256-gcm', symmetricKey, 12, encrypted));
default:
return callback(new Error('encryption algorithm ' + encryptionAlgorithm + ' not supported'));
}
Expand Down Expand Up @@ -237,24 +257,34 @@ function encryptWithAlgorithm(algorithm, symmetricKey, ivLength, content, encodi
var cipher = crypto.createCipheriv(algorithm, symmetricKey, iv);
// encrypted content
var encrypted = cipher.update(content, encoding, 'binary') + cipher.final('binary');
return callback(null, Buffer.concat([iv, Buffer.from(encrypted, 'binary')]));
var authTag = algorithm.slice(-3) === "gcm" ? cipher.getAuthTag() : Buffer.from("");
//Format mentioned: https://www.w3.org/TR/xmlenc-core1/#sec-AES-GCM
var r = Buffer.concat([iv, Buffer.from(encrypted, 'binary'), authTag]);
return callback(null, r);
});
}

function decryptWithAlgorithm(algorithm, symmetricKey, ivLength, content) {
var decipher = crypto.createDecipheriv(algorithm, symmetricKey, content.slice(0,ivLength));
decipher.setAutoPadding(false);

if (algorithm.slice(-3) === "gcm") {
decipher.setAuthTag(content.slice(-16));
content = content.slice(0,-16);
}
var decrypted = decipher.update(content.slice(ivLength), null, 'binary') + decipher.final('binary');

if (algorithm.slice(-3) !== "gcm") {
// Remove padding bytes equal to the value of the last byte of the returned data.
// Padding for GCM not required per: https://www.w3.org/TR/xmlenc-core1/#sec-AES-GCM
var padding = decrypted.charCodeAt(decrypted.length - 1);
if (1 <= padding && padding <= ivLength) {
decrypted = decrypted.substr(0, decrypted.length - padding);
} else {
callback(new Error('padding length invalid'));
return;
}
}

return Buffer.from(decrypted, 'binary').toString('utf8');
}
Expand Down